1. Field of the Invention
The present invention relates to a receiver for receiving text-based multiplex broadcasts.
2. Description of Related Art
For example, in Japan, FM broadcasts called "FM text-based multiplex broadcast" are realized in which character information data or the like are multiplexed and transmitted together with the original audio broadcast program.
Such FM text-based multiplex broadcast is called a Data Radio Channel (DARC) method, the development of which NHK Broadcasting Technology Research Institute has played a key role. The multiplexing standard for digital data such as character information is as follows: a subcarrier frequency of 76 kHz, a transmission rate of 16 kilobits per second, a modulation method of Level Controlled Minimum Shift Keying (LMSK), and an error correction method using a (272,190) compacted difference set cyclic code.
Program services such as character information can be classified into levels 1, 2 and 3. In all three cases, character information or the like is displayed using a dot display. In level 1, the information is provided as character information targeted as a service for a receiver capable of displaying 15.5 characters.times.2.5 lines, including a header. In level 2, the information is provided as characters or figures targeted as a service adopting a receiver capable of displaying 15.5 characters.times.8.5 lines, including a header. Level 3 is for traffic information services provided for receivers capable of displaying detailed maps from a CD-ROM (Compact Disc Read-Only Memory) or the like, namely, navigation systems.
Level 1 program services can be utilized for news, weather forecasts, traffic information, entertainment, main supplemental programs and the like. In this case, entertainment would include services providing fortune telling, messages from listeners, quizzes, town information and the like.
A main supplemental program provides information for supplementing a program such as the song name, performers name and telephone and fax numbers for requests when the original audio broadcast program is, for example, a music program. The main supplemental program will be hereinafter referred to as "program information" or "program linkage".
In addition to the above services, "emergency information" may also be provided as required at the time of emergencies.
FIG. 5 shows the frame structure of an LMSK signal which is multiplexed in the FM text-based multiplex broadcast of a DRAC method. One frame of this LMSK signal is comprised of 272 blocks, with each block comprising 288 bits.
One frame comprising 272 blocks is divided into 190 data packet blocks and 82 vertical parity packet blocks, with the vertical parity packet blocks being distributed and transmitted in the frame.
A 16-bit Block Identity Code (BIC) is attached to the head of each block. Four kinds of BIC are used for distinguishing each of the parity packets, and thus the heads of the frame can be discerned.
The data packet block has a 176-bit data packet following the BIC, after which a 14-bit Cyclic Redundancy Check (CRC) code is added, followed by an 82-bit horizontal parity check code.
In this case, the CRC code is attached for detecting residual errors after error correction using a product code. The vertical parity packet block is provided to have a 272-bit vertical parity packet following the BIC.
Each data packet comprises a 32-bit prefix followed by a 144-bit data block as shown in FIG. 6.
Furthermore, this prefix comprises a service identity code, a decode identity flag, an information end flag, a updating flag, a program number, a page number, a data link code and a data packet number, as shown in the lower portion of FIG. 6.
The service identity code consists of 4 bits and is for discerning the program contents and the like. Regarding level 1, "1" is general information for sequential reception processing, and "2" and "3" are general information for recording and reception processing.
In this case, the sequential reception processing is a mode for the receiver starting decoding processing for displaying on receipt of the first data packet of the program data or the page data. This sequential reception processing is carried out on the receiving side for a program where it is required to take timing of presentation on the receiving side or for a program where the information will not be displayed in time if the decoding processing is started after the last packet of the data group is obtained.
Further, recording and reception processing is a mode for not starting decoding processing for displaying until all of the data for the program data or the page data are received and recorded and then error correction is carried out using CRC code for every data group. Besides, the programs for performing this recording and reception processing include news, weather forecast, traffic information and so on.
In the prefix, the decode identity flag is one bit, and is "1" when the error correction circuit for the receiver outputs data by decoding in the horizontal direction only, and "0" when the data are outputted after decoding in the horizontal direction and the vertical direction.
Sequential reception processing, when the decode identity flag is "0", is defined in such a manner that decoding processing for displaying each of data packets is carried out at the time when the receiver receives the BIC at the head of the 302nd packet from the reception of the BIC at the head of respective data packets.
The information end flag is one bit and is "1" when transmission of a data group with a certain data group number is completed, and "0" when this is not the case. The updating flag is two bits, and is incremented by one every time a data group is updated. The program number is 8 bits, and the page number is 6 bits, with the data group number being formed using both of these items.
Furthermore, the program number is from 0 to 255, the "main menu" being assigned to "0" optional programs such as news and weather forecast being assigned to 1 to 253, the main supplemental program (program information or program linkage) being assigned to "254" and emergency information being assigned to "255".
Further, the page number is from 1 to 62, i.e., one program can have a maximum of 62 pages. One page corresponds to one to four of data groups, with one data group comprising one or a plurality of data blocks.
Furthermore, the data link code is 2 bits and is used for linking each group of the divided data group. When the data are so large that the number of the data packets belonging to one data group exceeds the maximum value of the data packet number, the data group is divided into a maximum of 4 groups with different data link codes. The data group is then transmitted with the divided groups of the same group number and different data link codes being linked in the order of the code numbers 0.fwdarw.1.fwdarw.2.fwdarw.3.
The data packet number is 8 bits long, and is aligned in sequence from "0". The data packet number indicates the sequence of the data packets in one program. That is, the data packet number indicates in which position the data packet is placed in one program.
At level 1, one page is usually displayed in the form of 15.5 characters.times.2.5 lines, but can also be displayed in the form of 15.5 characters.times.8.5 lines. Further, in this case, the character data are for displaying characters defined by Japanese Industrial Standard Code (JIS code).
On the other hand, as described above and as shown in FIG. 7A, one data group is made up of one or a plurality of data blocks of the data packet. In this case, the data blocks having equal service identity code, data group number and update flag arranged in the order of the data packet number from a data block having a data packet number 0 to a data block where an information end flag of the prefix is set form one data group.
Thus, the data group has the length integer times as long as 144 bits which is the length of the data block. Further, one data group corresponds to one display unit, i.e., display data in one page.
Further, as shown in FIG. 7B, 8 bits at the head of the data group represent a heading start code showing the start of that data group, the following 16 bits are a data group header having a flag showing the existence of linkage of data groups and the byte number of the following data group data. Furthermore, null codes for adjusting the length of the data group to integer times of 18 bytes follows the data group data, then a data group end code showing the end of the data group follows, and finally a CRC code for detecting errors of the data group follows.
Further, one program is composed of one program data, but, as shown in FIG. 8A, the program data are composed of a plurality of data groups, the data group at the head is program control data and all of the remaining data groups are page data.
Further, the program control data are composed of a program data header in 6 bytes and a data unit group as shown in the left portion of FIG. 8B. Then, the program data header has such data as shown in the left portion of FIG. 8C, but, for example, the third byte shows a program number, 6 bits in the lower position of the fourth byte shows the total number of pages of the program, the fifth byte shows a presentation function and 4-bits in the higher position of the sixth byte shows an information type.
Besides, the presentation function at the fifth byte shows a type of the code included in the program and the function of display, and respective bits are assigned as shown in FIG. 9. For example, the first bit (LSB) becomes "1" in the case of character data, and the second bit becomes "1" in the case of figure data. Further, for a general program, all data of the program are received, and displayed sequentially from the first page, and for a non-general program, even when all data of the program cannot be received, display is made sequentially from a page that can be displayed.
The information type in 4 bits in the higher position of the sixth byte shows whether the information is free of charge or charged and so on.
Further, the data unit group is composed of a plurality of data units having character data and figure data for display as shown in FIG. 10. Besides, one of these data units is used as a selection control data unit, and includes a key-in number, a destination page number, a destination program number, a destination service identity code and so on.
Furthermore, the page data are composed of a page data header in 7 bytes and a data unit group as shown in the right portion of FIG. 8B. In this case, the page data header has such data as shown in the right portion of FIG. 8C, wherein the third byte shows a program number, 6 bits in the lower position of the fourth byte show a page number in that program, the fifth byte shows a presentation function and 4 bits in the higher position of the sixth byte show an information type.
The foregoing expresses a format in text-based multiplex broadcasts by a DARC method.
Further, as described above and as shown in FIG. 11, the receiver compatible with level 1 has a display element 50 such as an LCD having a display screen capable of displaying 15.5 characters.times.2.5 lines (248 dots in width by 44 dots in length). However, in the display screen of the display element 50, the 0.5 line portion of the upper portion of the display screen 50a is for displaying a header text, and the 2 lines portion of the lower portion is a text display screen 50b.
When the receiver receives text-based multiplex broadcasts, the main menu is displayed on the display element 50 as shown in FIG. 12A. Here, FIG. 12A shows a state that the main menu covers a plurality of pages and first one page among them is displayed. Besides, displayed on the display screen 50a of the header text are the broadcasting station name which is broadcasting the text-based multiplex broadcast which is currently being received by the receiver, the service (company) name of the text-based multiplex broadcast, and the menu name.
When a predetermined key operation is performed in such a state, the next page is displayed on the text display screen 50b as shown in FIG. 12B.
When the user decides upon the number of an item that the user wishes to see from the main menu, then the menu of the selected item is further made to be displayed. For example, when the user selects "3. WEATHER FORECAST" from within the main menu, then the contents "1. TODAY'S WEATHER", "2. TOMORROW'S WEATHER" are displayed as shown in FIG. 12C.
Furthermore, when the user decides upon the number of an item that the user wishes to see from within the menu, then the first page of the selected item is made to be displayed. For example, when the user selects "1. TODAY'S WEATHER" from the menu, specific character information relating to the "1. TODAY'S WEATHER" is displayed, as shown in FIG. 12D.
Besides, FIGS. 12A to 12D show displays in Japanese in compliance with the JIS standard. For reference, the displays of FIGS. 12A to 12D in English are shown in FIGS. 13A to 13D, respectively.
As described above, there are sequential reception processing and record reception processing in the FM text-based multiplex broadcast, and a broadcasting station controls the display timing in the case of a program of sequential reception processing. As a result, automatic page feed is carried out for the display of programs.
As against the above, in the case of a program of record reception processing, the display is not altered even when all the data required for display are received, and page feed is made when the user performs key operation. Namely, manual page feed is started.
However, it is inconvenient in use in case the method of page feed is different depending on the program.